1. Technical Field
The present invention relates to an image forming apparatus such as a copier and a printer using electrophotographic system, and in particular relates to an image carrier unit that is removably loaded into an image forming apparatus and is provided with an image carrier such as a photoreceptor and a charge roll that charges a surface of the image carrier, and to an image forming apparatus provided with the image carrier unit.
2. Related Art
Conventionally, devices using the corona discharge phenomenon, such as scorotron chargers, have come to be widely used as charge devices in image forming apparatus such as copiers and printers using the electrophotographic system. But in the case of charge devices utilizing the corona discharge phenomenon, the generation of ozone and nitrogen oxide, which are harmful to humans and Earth's environment, is becoming a problem. In contrast, contact charging, where a conductive charge roll is brought into direct contact with a photoreceptor to charge the photoreceptor, has become mainstream recently because there are considerably few occurrences of ozone and nitrogen oxide and it is power-efficient.
In contact charging, the charge roll is pressed against the photoreceptor with constant pressure by a spring. When the charge roll is left in this state over a long period of time, sometimes this causes permanent distortion in the portion where the charge roll contacts the photoreceptor, as the result the charging ability changes and image defects such as density unevenness occur, or the photoreceptor and the charge roll rub against each other due to vibration and the line during transport, and image quality defects such as density unevenness occur due to damage to the charge roll.